The requirements to be met by electromagnetic pumps vary with the field of application. They include high working pressure, increased efficiency, simple manufacture and high operational reliability. Specific parameters such as pump duct pressure per unit length and mass per unit power are essential to evaluating pump construction inasmuch as, eventually, they influence the cost of both the pump and its associated plant, as may be the case with transport power plants.
Nowadays particular attention is paid to development of electromagnetic induction pumps wherein the induction principle of action upon an electrically conductive liquid is carried out by an electromagnetic force produced in the conductive liquid due to interaction of a magnetic field set up by a pump inductor and an electric field induced in the conductive liquid.
The induction acting upon the conductive liquid is produced by two methods: first, a magnetic field varying with time and space (a running or rotating field) is set up by an inductor in the conductive liquid; second, a magnetic field varying only with time (a pulsating field) is set up in the conductive liquid by an inductor.
The first method requires an inductor of complicated construction, with the winding thereof distributed in the direction of the conductive liquid flow and installed in inductor slots after the manner of the stator of an asynchronous electric machine. The inductor winding is situated in the immediate vicinity of the duct for the conductive liquid flow and, therefore, handling liquid metals at a high temperature adversely affects the operational dependability of the pump. Low pressure developed per unit length of the inductor due to low magnetic induction in the duct resulting from saturation of the inductor teeth necessitates an increase of the pump dimensions in the direction of the conductive liquid flow. Lastly, the production of a distributed-winding inductor requires special equipment, which leads to a high pump cost.
With the second method, use is made of pulsating magnetic field inductors, which are very simple in construction, being essentially constituted by a magnetic circuit with customary transformer excitation windings. Inasmuch as the magnetic circuit has no tooth zone, substantial magnetic field induction can be produced in the conductive liquid being pumped, and therefore substantial pressure can be developed within a short length of the inductor. Furthermore, in such an inductor, the winding can be situated outside the zone of action of high temperature of the liquid being pumped, whereby the operational reliability of the pump is enhanced.